1. Field of the Invention
This invention relates generally to a printing machine, and more particularly concerns a toner level sensing apparatus for detecting the presence or absence of particulate matter or liquid, such as toner, relative to a preselected level in a container.
2. Description of the Prior Art
Generally, in a printing process, such as an electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive surface is exposed to a light image of an original document being reproduced. This records an electrostatic latent image on the photoconductive surface. After the electrostatic latent image is recorded on the photoconductive surface, the latent image is developed by bringing a developer mixture into contact therewith. A common type of developer mixture comprises carrier granules having toner particles adhering triboelectrically thereto. This two-component mixture is brought into contact with the photoconductive surface. The toner particles are attracted from the carrier granules to the latent image. This forms a toner powder image on the photoconductive surface, the toner powder image being transferred subsequently to a copy sheet. Finally, the toner powder image is heated to permanently fuse it to the copy sheet in image configuration.
A high speed commercial printing machine of this type uses a magnetic brush development arrangement for developing the latent image. The magnetic brush arrangement generally employs several developer rollers, disposed in a developer housing, for transporting the developer mixture closely adjacent to the photoconductive surface. Augers are usually used to mix and disperse developer materials throughout the developer housing.
In one exemplary magnetic brush arrangement, toner is conveyed to the developer housing by way of a feed system, the feed system including a toner supply bottle and a toner dispenser. The toner dispenser, which includes a housing or hopper, serves as an interface between the toner supply bottle and the the developer housing. After a given period of use, the toner in the toner supply bottle is dispensed, and the toner supply bottle is either replenished or replaced.
To determine when the toner in the toner supply bottle or hopper has dropped below a desired level, various known developing arrangements employ a level sensor, the level sensor being disposed in either the developer housing or the toner dispenser housing. The disclosures of the following patents may be relevant to various aspects of the level sensor of the present invention; U.S. Pat. No. 3,498,500 to Hansen issued Mar. 3, 1970; U.S. Pat. No. 3,834,806 to Whited issued Sep. 10, 1974; U.S. Pat. No. 3,896,279 to Sugawara issued Jul. 22, 1975; U.S. Pat. No. 3,920,154 to Sugawara issued Nov 18, 1975; U.S. Pat. No. 3,920,155 to Whited issued Nov. 18, 1975; U.S. Pat. No. 3,979,022 to Whited issued Sep. 7, 1976; U.S. Pat. No. 4,159,786 to Biddie,III et al. issued Jul. 3, 1979; U.S. Pat. No. 4,626,096 to Ohtsuka et al. issued Dec. 2, 1986.
U.S. Pat. No. 3,498,500 discloses a level sensing controller for determining the quantity of xerographic toner powder in a toner dispenser of an automatic xerographic reproducing machine. First and second electro-audio transducers are mounted on opposing ends of a toner dispenser housing. The second transducer is coupled to a threshold detecting circuit and is adapted to function as a receiver. An acoustical signal is transmitted by way of the first transducer. If the toner in the dispenser housing is below a preselected level, the signal is received at the second transducer and the detecting circuit is triggered.
U.S. Pat. No. 3,834,806 and U.S. Pat. No. 3,920,155 disclose a level indicating apparatus, a portion of which is mounted in a toner particle storage housing. The housing has a tubular member in which toner particles are capable of being stored. A planar member is suspended within the tubular member and the planar member is coupled to a magnetic pick-up. The magnetic pick-up senses the movement of the planar member when the planar member contacts toner particles. A low level signal is generated when the planar member is no longer in contact with the toner particles.
U.S. Pat. No. 3,896,279 describes a pair of opposed blades mounted on a rotor. The blades are supported by the toner in the housing. As the toner supply is depleted, the rotor pivots the blades toward the horizontal. When the blades reach the horizontal, a switch is actuated which, in turn, energizes a display to warn an operator of impending toner exhaustion.
U.S. Pat. No. 3,920,154 teaches a detector for sensing that the level of toner particles in a housing has dropped below a predetermined level. A flexible member extending across the reservoir actuates a switch in response to the toner level being below the predetermined level. The switch energizes a lamp warning the operator of this condition.
U.S. Pat. No. 4,159,786 discloses a toner level sensor including a cantilevered sensor rod mounted to a trough in which toner is capable of being stored. A decorator roll, having a plucking pin mounted thereto, is rotatably mounted in the trough. As the roll rotates the plucking pin contacts an end of the rod and causes the rod to vibrate. The frequency of the rod vibration varies as a function of the level of toner in the trough.
U.S. Pat. No. 4,682,874 discloses a detector positioned within an enclosure, the detector being adapted to sense the level of particles, such as toner, being advanced by a helical auger. The detector includes a switch having an elongated actuator arm, the actuator arm resting on the particles being advanced by the helical auger. When particles are being transported by the helical auger, the actuator arm is raised to an upward position for closing the switch. When the particles being transported are beneath a preselected level, the actuator arm moves downwardly to open the switch.
U.S. Pat. No. 4,626,096, in its "Background" section discloses a known sensor or piezo-electric element disposed in a toner hopper. The output of the piezo-electric element varies as a function of the weight applied to the element. When the level of the toner reaches a preselected level, the output of the element drops below a reference voltage and an indicating lamp is activated.
A number of the above-described detectors or sensors are not necessarily designed for convenience or compactness. That is, many of these detectors or sensors are not housed in an integrated package that can be installed, with a minimum amount of effort. Hence the manufacturing and installation costs associated with these sensors can be less than optimal. While the U.S. Pat. No. 4,682,874 detector is easy to manufacture and install, its application may be somewhat limited. In particular, the detector typically includes an arm that is positioned above the toner and adjacent the auger. For various toner enclosures, however, it may be undesirable to locate the level sensor adjacent the auger. Additionally, the noise immunity of at least some of these sensors can fall far short of being ideal. For example, the sensor rod of U.S. Pat. No. 4,159,786, is mounted to the tough and is therefore capable of being vibrated inadvertently whenever the trough is vibrated. Such Inadvertent vibration can generate false signals that indicate incorrectly a low toner state. Finally, the piezo-electric element discussed in U.S. Pat. No. 4,626,096, under certain circumstances, cannot sense accurately a low toner state. In particular, even when the overall level of toner in the hopper is low, the element will not sense that low level if the distribution of the toner is non-uniform and the sensor is covered by toner.
It would be desirable to provide a detector or sensor that is manufactured in a single low-cost unit, the low-cost unit being mounted readily in many different types of enclosures. Moreover, the sensor would be highly sensitive and accurate while possessing a great degree of noise immunity.